Sunday, April 24, 2016

Fitness level and a fib risk: finding the sweet spot

CRF, as assessed by maximal oxygen
uptake (VO2max) during exercise testing, was measured at baseline in
1950 middle-aged men (mean age 52.6 years, SD 5.1) from the Kuopio
Ischaemic Heart Disease (KIHD) study.

Results

During average follow-up of 19.5 years,
there were 305 incident AF cases (annual AF rate of 65.1/1000
person-years, 95% confidence interval [CI] 58.2–72.8). Overall, a
nonlinear association was observed between CRF and incident AF. The
rate of incident AF varied from 11.5 (95% CI 9.4–14.0) for the
first quartile of CRF, to 9.1 (95% CI 7.4–11.2) for the second
quartile, 5.7 (95% CI 4.4–7.4) for the third quartile, and 6.3 (95%
CI 5.0–8.0) for the fourth quartile. Age-adjusted hazard ratio
comparing top vs bottom fourth of usual CRF levels was 0.67 (95% CI
0.48–0.95), attenuated to 0.98 (95% CI 0.66–1.43) upon further
adjustment for risk factors. These findings were comparable across
age, body mass index, history of smoking, diabetes, and
cardiovascular disease status at baseline.

Conclusion

Improved fitness as indicated by higher
levels of CRF is protective of AF within a certain range, beyond
which the risk of AF rises again. These findings warrant further
replication.